Hydrophilic and partially hydrophilic plastic materials for use in the manufacture of contact lenses are extensively described in the literature. For example, U.S. Pat. Nos. Re. 27,401, 2,976,576; 3,499,862; 3,503,942; 3,361,858; 3,699,089 and 3,822,089 describe processes for producing three dimensional, sparingly crosslinked, polymeric materials and/or contact lenses of such materials. These materials have the extraordinary ability to absorb water with concomitant swelling to a soft mass. The resulting hydrogel material is characterized by good mechanical properties, complete transparency, high resistance to degradation in boiling water, inertness, good optical geometry and shape retention. Given the fact that wearers of soft contact lenses experience a comfort not heretofore obtained with hard contact lenses, i.e., poly (methyl methacrylate), it is small wonder that the soft contact lens industry has displayed remarkable growth during the 1970's, and forecasts indicate further vibrant growth for the 1980's.
However, one of the problems associated with soft contact lenses concerns sterilizing and cleaning them. The very property of soft lenses which permit them to absorb sizeable quantities of water, e.g., upwards of 38 weight percent water based on the total weight of the hydrogel, also allows preservatives which might otherwise be used for cleaning and sterilizing to be absorbed or even concentrated or later released when the soft contact lens is on the eye. This can have the harmful result of damaging or staining the contact lens itself, and/or harming the sensitive tissues of the conjunctivae or cornea.
As pointed out in U.S. Pat. No. 3,954,965 issued May 4, 1976, hard contact lenses do not absorb appreciable amounts of water (about 0.1 to 4%) and thus, the use of effective preservatives does not create a problem in the hard contact lens field. However, users of soft contact lenses are warned not to use solutions designed for hard contact lenses for the reason that the preservative in such solutions will be absorbed and even concentrated by the soft lens resulting in possible serious damage to the soft lens/or eye; see U.S. Pat. No. Re. 29,693, issue date July 4, 1978.
The normal regimen with respect to soft lens care dictates proper cleaning and sterilization. Proteinaceous deposits tend to form and build on the lenses during wear and handling. The art suggest the use of various enzymatic cleaners such as papain or pancreatin to effectively remove such deposits. The cleaning step does not kill bacteria and other microorganisms. Therefore, a sterilization procedure which may be thermal or chemical is normally performed after the cleaning step. Thermal sterilization generally involves boiling the lens in isotonic saline solution. Chemical sterilization can be effected by soaking the lenses in solutions of chemical sterilizing agents, for example, chlorhexidine and/or thimerosal.
Accordingly it is an object of the present invention to provide an aqueous disinfectant solution for soft contact lenses which is non-toxic and nonirritating to the eye, is an effective anti-bacterial agent, and does not adsorb or penetrate into the soft contact lens.